The invention relates to an electrolytic capacitor comprising a stack of capacitor elements, each capacitor element comprising an anode foil having a dielectric oxide layer as well as a cathode contact layer having a solid electrolytic material.
The invention also relates to a method of manufacturing an electrolytic capacitor, in which capacitor elements are manufactured from an anode foil having a dielectric oxide layer on which a cathode contact layer having a solid electrolytic material is provided, after which a number of capacitor elements are formed into a stack.
In British Patent GB No. 1225601 a description is given of an electrolytic capacitor and a method of manufacturing thereof, in which a foil of a valve metal, for example aluminium or tantalum, is provided with a non-porous oxide film and coated by precipitation with a layer of a solid electrolytic material in the form of an electrically conductive complex salt of tetracyanoquinodimethan (TCNQ) in a polymer binder. A cathode contact strip is embedded in the solid electrolytic material, after which a roll or a stack of foils is formed.
For the manufacture of compact capacitors having homogeneous electrical properties a construction having a multilayer structure in the form of a stack of uniform capacitor elements is preferred. This is important, for example, for use in high frequency ranges. The electrolytic capacitor described in said British Patent Specification cannot be readily manufactured in a multilayer structure. The manner in which the cathode contact is provided is not very reliable. Due to the presence of a polymeric binder the solid electrolytic material exhibits a reduced conductivity and the contact with the oxide film is unsatisfactory, in particular in the (narrow) pores of the anode foil. Pores in the anode foil increase the surface area of the foil and, consequently, the capacitance of the capacitor.